1. Field of the Invention
The present invention relates to the packaging of electronic components, especially components whose surface needs to be unoccupied such as surface acoustic wave (SAW) filters, RF components, sensors and, more specifically, the method for making a packaging of this kind.
Surface wave components (SWC) used in electronics, especially as filters in the radiofrequency domains or intermediate frequency domains, in order to select frequency bands in mobile telephony, make use of the principle of the generation and propagation of acoustic waves on the surface of a piezoelectric substrate. This function makes it necessary to prepare a free space on the surface of the component on which the acoustic waves are propagated. Thus, the standard methods for the protection of surface acoustic wave components use hermetically sealed ceramic or metal packs. However, these methods are costly and unproductive, and make it difficult to minituarize the components.
2. Description of the Prior Art
In the field of semiconductor components, assembling technologies known as CSP (for Chip-Size Package or Chip-Scale Package technologies) give a high degree of miniaturization. The technology that is presently most worthwhile in terms of degree of miniaturization and cost is based on a flip-chip mounting technique (known to those skilled in the art) as illustrated in FIG. 1.
More specifically, a semi-conductor component 1 is attached to a base 2 by means of xe2x80x9cflip-chipxe2x80x9d type contacts 11 and 12. Electrical pads 21 and 22 connect the entire component 1 to external circuits by internal metallizations and via holes through the base. An encapsulation resin (not shown) consolidates the mechanical assembly and protects the component.
However, this method is not directly applicable to surface-wave components: the encapsulation resin fills the interstice between the component and the base. This disturbs the propagation of the surface acoustic waves. Secondly, since the active surface is not passivated, unlike the semiconductor components, the resin by itself is not a sufficient barrier against external attack from agents such as moisture.
In the more particular field of surface acoustic wave filters, the firm Siemens Matsushita Components GmbH has proposed the packaging of components by the fabrication of a sheath forming caps that surround the chips and lie on the substrate in regions between the chips (WO 99/43084). The caps may be obtained from a metal foil fixed to a weldable frame of the base, or a plastic foil bonded to the base between the chips. In the case of a plastic sheet, even if it is metallized, the shielding is neither hermetically sealed nor perfectly shielded.
The present invention proposes to collectively sheath the chips with a deformable plastic film that will adhere to the back and sides of the chips as well as to the substrate. This method has the advantage of boosting the mechanical strength of the chip on the base. It also has the advantage wherein, after a step described here below for the local elimination of the film, it presents a structure on which it is easy to make a continuous mineral deposit that perfectly seals the structure. Finally, if the mineral deposit is chosen to be metallic, a continuous electromagnetic shielding is made, and this shielding could be in direct contact with the electrical ground on the substrate.
The deformable film, adgering to the rear face and the side faces of the chips as well as to the base between teh chips, forms a monolithic unit with high mechanical strength.
More specifically, an object of the invention is a method for the packaging of electronic components, comprising the following steps:
The mounting of at least one electronic component on its active face side to a base, said base comprising electrical contacts on a first face and connection pads on a second face, and comprising a series of via holes connecting the electrical contacts and the connection pads and a series of holes.
The deposition of a deformable film on the face opposite to the active face of the electronic component or components.
The aspiration of the deformable film through the series of holes from the second face of the base, so as to sheath said electronic component or components and place these components in contact with the deformable film so as to form a solid assembly.
According to one variant of the invention, the method of the invention may furthermore include a step for the total elimination of the film on the base in the zone between the chips enabling the mineral deposit to totally sheath the component and thus provide perfect hermetic sealing quality. In the case of a metal deposit, this step also provides for the resumption of an electrical ground contact on the substrate and thus provides for efficient electromagnetic shielding.
An object of the invention is also a method for the batch manufacture of packaged electronic components comprising the following steps:
The batch mounting of electronic components on the active face side to a base, said base comprising electrical contacts on a first face and connection pads on a second face, and comprising a series of via holes connecting the electrical contacts and the connection pads and a series of holes.
The deposition of a deformable film on all the faces opposite the active faces of the electronic components.
The aspiration of the deformable film through the series of holes from the second face of the base, so as to sheath said electronic components
The deposition of an encapsulating resin on the deformable film so as to provide hermetically sealed protection for the electronic components.
The cutting out of the unit formed by the resin/deformable film/base so as to individualize the packaged electronic components.
According to one variant of the invention, the component or components are surface acoustic wave devices.
Advantageously, the aspiration of the deformable film is coupled with a heating step and/or a step for the application of a pressure to the surface of the deformable film.
According to one variant of the invention, the packaging method furthermore comprises a deposition of a mineral layer to provide hermetic sealing on top of the deformable film.
Advantageously, the packaging method may also include a conductive deposition on top of the deformable film in order to provide for the shielding of the components.
The packaging method may also include the depositing of a second deformable film (that may be identical to the first deformable film) on top of the conductive deposit. It may advantageously be a polymer film charged with conductive mineral particles. This second film may thus replace the standard packaging resin in contact with the exterior.